Centerline of a road is a line representing the physical center of a roadway between road shoulders. It often coincides with the center painted line dividing bi directional travel lanes.
Until 1971, white center lines were used in the United States. However the 1971 edition of the Manual on Uniform Traffic Control Devices, mandated yellow as the standard color of center lines nationwide. Yellow was adopted because it was already the standard color of warning signs.
In the United States, two states claim to be the first to have developed center lines. According to the state of Michigan, painted white center lines were developed by Edward N. Hines, the chairman of the Wayne County, Michigan, Board of Roads. According to the state of California, Dr. June McCarroll developed center lines in 1917.